Respiratory Diseases Quiz

Ventilation & Perfusion

• Ventilation (V) refers to the movement of air into and out of the lungs.
• It involves the rate at which air enters and leaves the lungs.
• Ventilation ensures the delivery of oxygen (O2) to the alveoli and removal of carbon dioxide (CO2) from the body.
• Two types of ventilation exist: pulmonary and alveolar.

Pulmonary Ventilation

• Pulmonary ventilation (RMV) is the process of moving air in and out of the respiratory tract in a given minute during quiet breathing.
• It's also known as minute ventilation or respiratory minute volume.
• Pulmonary ventilation involves a cyclical process where fresh air enters the lungs, and an equal volume of air leaves them.
• Normal pulmonary ventilation is 6 L/minute.
• Calculated by multiplying tidal volume (TV) by respiratory rate (RR)
• Formula: Pulmonary Ventilation = Tidal volume × Respiratory rate
• Example: 500 ml × 12/min = 6000 ml/min

Alveolar Ventilation

• Alveolar ventilation is the amount of air used for gas exchange every minute.
• It's different from pulmonary ventilation.
• Pulmonary ventilation involves all the air moving in and out of the respiratory tract (6L/min), but not all of that air is used in gas exchange
• Alveolar ventilation only accounts for the volume of air exchanged in the alveoli.
• The air trapped in the respiratory passage (called dead space) is not used in gas exchange

Calculation for Alveolar Ventilation

• Normal alveolar ventilation is 4200 ml (4.2 L)/min.
• Formula: Alveolar Ventilation = (Tidal volume – dead space) x Respiratory rate.
• Example: (500 – 150) ml × 12/min = 4200 ml/min

Dead Space

• Represents the part of the respiratory tract where gas exchange does not occur.
• Air present in dead space is named dead space air.
• Two types of dead space:
  • Anatomical dead space
  • Physiological dead space

Anatomical Dead Space

• Extends from the nose up to the terminal bronchiole.
• Includes the nose, pharynx, trachea, bronchi, and their branches up to the terminal bronchioles.
• These structures are only passages for air movement.
• Gas exchange does not occur in these structures

Physiological Dead Space

• Includes anatomical dead space plus two additional volumes which do not function for gas exchange.
• 1. Air in the non-functioning alveoli due to respiratory diseases (like damaged alveoli) or dysfunction of the alveolar membrane.
• 2. Air in alveoli not receiving adequate blood flow (inadequate blood supply).
• These two volumes represent wasted ventilation

Perfusion (Q)

• Perfusion (Q) is the flow of blood through the pulmonary capillaries.
• It allows the transport of oxygen (O2) from the alveoli to tissues and the return of carbon dioxide (CO2) to the lungs.
• Pulmonary circulation maintains perfusion with low pressure.

Ventilation-Perfusion Ratio

• Ventilation-perfusion ratio (VA/Q) is the ratio of alveolar ventilation to the amount of blood perfusing the alveoli.
• It showcases the relationship between the amount of air entering the alveoli (VA) and the blood flowing through the surrounding capillaries (Q).
• Normal value is 0.84.

Normal Value of Dead Space

• Under normal conditions, the normal volume of dead space is 150 ml.
• Physiological dead space is equivalent to anatomical dead space.
• All alveoli function properly, receiving adequate blood flow.
• Physiological dead space increases during respiratory diseases affecting pulmonary blood flow or alveoli.